The present invention relates to a semiconductor vapor phase growing apparatus, specifically to a barrel type epitaxial vapor phase growing apparatus.
FIG. 1 illustrates a longitudinal sectional view of a conventional barrel-type of epitaxial vapor phase growing apparatus. In the figure, a bell-jar 11 made of quartz defines a reaction chamber 12 closed at the top by a seal plate 20 made of stainless steel and a ring 19 of stainless steel with O-ring packings 18 and 18A between a flange 17 at the top of bell-jar 11 and plate 20. Seal plate 20 has an opening 20A at its center through which hanger rod 25 hangs a susceptor assembly S rotatably mounted by a roller bearing assembly 20B on seal plate 20. An air-tight gear box 22 mounting a driving motor 23 thereon is also provided on plate 20. A gear 24 driven by a drive axis 23A of motor 23 meshes with a gear 26 fixedly connected on the top of hanger rod 25. A quartz baffle 21 hangs from seal plate 20 to cover and protect the inside surfaces of reaction chamber 12, seal plate 20 and ring 19 from corrosive gases such as Hydrogen Chloride (HCl) or Silicon Tetrachloride (SiCl.sub.4) flowing into reaction chamber 12 from a nozzle 27 mounted on ring 19.
Susceptor assembly S includes a carbon top plate 13 fixed at the lower end of hanger rod 25, a carbon bottom plate 14. The circumferences of plates 13 and 14 are formed as a polygon, for example hexagonal or octagonal, and a plurality of carbon plate susceptors 15 extend therebetween. Each susceptor 15 is located between top plate 13 and bottom plate 14 with a slight slope outwardly with respect to the downward direction. On the surface of each susceptor 15 is provided a plurality of small recesses in which a semiconductor substrate 16 (hereinafter called a wafer) is mounted for treatment. Outside of bell-jar 11, a plurality of infrared ray lamps 30 surrounded by a cover 30A heat susceptors 15 and wafers 16. Outlet 31 exhausts gases from reaction chamber 12.
As mentioned above, ring 19 mounts nozzle 27 in an air tight connection, through which reaction gases such as Dichlorosilane (SiH.sub.2 Cl.sub.2) or Silicon Tetrachloride (SiCl.sub.4) flow into reaction chamber 12. Seal plate 20 mounts an inlet 28 in an air-tight connection, through which purge gases such as nitrogen gas (N.sub.2) or hydrogen gas (H.sub.2) flow into reaction chamber 12 through a gap 21A between seal plate 20 and baffle 21. Also, on the side plate of gear box 22, an inlet 29 for purge gases such as "N.sub.2 " or "H.sub.2 " is mounted in air tight connection, through which the purge gases flow into the inside of gear box 22. The purge gases inside of gear box 22 flow through bearing 20B into reaction chamber 12. The flow of purge gases from inlets 28 and 29 into reaction chamber 12 prevents reaction gases from invading gear box 22 and gap 21A between seal plate 20 and baffle 21, and prevents reaction gases corroding seal plate 20, bearing 20B and gears 24 and 28.
In the conventional type of epitaxial vapor phase growing apparatus mentioned above, the purge gases from inlet 29 flowing through gear box 22 and bearing 20B into reaction chamber 12 carry particles of dust from the driving mechanism including gears 24 and 26, bearing 20B, etc. Those particles of dust adhere to the surface of wafer 16 reducing the quality of the wafer. Furthermore, they produce "auto doping" and lowered resistance values in the wafer.